[dmjlambert]

An electric motor with bad bearings that is not directly attached to the engine would squeal or grind but not change with engine RPMs/Acceleration, and it would also normally come on with the engine started or key on. So that would be my top suspect, a bad electric motor. The only electric motor like that on a stock truck is the blower motor. But some folks have put in accessories, such as electric fans on the radiator.